This invention relates to guiding magnetic storage tape along a tape path.
Tape cartridges for tape carrying digital data on a number of tracks across a magnetic tape are well known. There are generally three types of such data storage cartridges. Single reel cartridges comprise a spool of tape which is provided to a user along with a leader block positioned at one end thereof. In operation, the user places the spool in a drive mechanism which functions to thread the tape for receipt by another reel. The tape is transported between the two reels and data is read and/or written. The drive mechanism is responsible for providing guiding of the tape as it passes by a head such as, for example, a transducer. The drive mechanism also functions to provide tape tension by, for example, servoing the reels as they change their diameters during the read/write process.
Dual reel data cartridges, also called xe2x80x9chub-drivenxe2x80x9d cartridges, include two or more spools or xe2x80x9chubsxe2x80x9d integral to the cartridge. Placement of the hubs within the cartridge itself obviates the time and effort required for tape threading and, therefore, permits significantly faster access over conventional single reel cartridges. The internal placement of the hubs further permits the use of an external protective covering or shell which functions to protect the hubs and the tape from contaminants during both storage and use. In operation, respective drive motors engage the spools. In further contrast to the aforementioned single reel cartridges, dual reel data cartridges also include tape guiding means for guiding the tape past the head or transducer. Typically, the guiding means comprises one or more rigid flanges such as fixed guides or pins. See, for example, U.S. Pat. No. 5,870,924 to Fahimi et. al., which discloses a tape bearing surface usable as a front guide assembly.
Belt-driven data cartridges, like dual reel cartridges, incorporate the tape within the cartridge itself and include two or more spools or hubs. Unlike dual reel cartridges, belt-driven data cartridges further include an elastic drive belt operative to engage the tape at the respective tape-spool peripheries and provide tape tension. More specifically, tape cartridges of this type include a cartridge shell that defines an enclosure, and a pair of tape reels supported within the enclosure. A length of magnetic tape extends along a tape path within the enclosure. Each end of the tape is wound onto one of the reels. Like dual reel cartridges, the tape moves past suitable guides or flanges and across an opening in an edge of the cartridge into which a read/write head or transducer protrudes to tension the tape and write or read data when the cartridge is inserted into a recording/reproducing machine.
Regardless of the type of data cartridge used, the process for reading and writing data remains substantially the same. That is, data is written across all or substantially all of each respective track. Data is read, however, from only a portion of each track. In this manner, allowances can be made for read errors resulting from shifts in the magnetic tape. As those skilled in the art will recognize, such shifts, called track misregistrations (TMRs) may be caused by numerous events such as, for example, slamming of a tape edge against a fixed flange (reference edge), tolerance differentials between one or more tape guides and the data cartridge substrate, etc. Any one or more of these events may result in an off-track event.
In prior art data cartridges where tracks were written linearly on magnetic tapes, a small number of relatively wide data tracks (10 or less) were used. Conventional methods for tape edge guiding were, therefore, generally sufficient. As long as the tape was maintained within a predetermined critical area, data could be written and read consistently.
Advances in tape manufacture, coupled with the desire to read and write more information on individual cartridges, however, has altered the control scenario dramatically. Presently, data cartridges have substantially more data tracks (100 or more), each of which is substantially narrower (micrometers in width) than prior art linear written tracks. As a result, much tighter control is necessary to prevent off-track events.
To ensure that the cartridge tapes are properly positioned so that each of the very narrow individual tracks having data are appropriately positioned as they cross the read/write head, it is necessary that the tapes be guided precisely along their paths of travel. Closed loop systems have, therefore, been used for positioning data cartridge tapes. Such servo systems incorporate servo tracks written on the magnetic tapes which are followed by a tracking head. The servo tracking head operates to control the position of the head or transducer to ensure that it is properly aligned with the tape. As TMRs cause the tape to move, the servo tracking head moves in step thus maintaining the head within the critical read area of the tape.
Although servo systems have greatly addressed the problems associated with off-track events, they have created new control problems of their own. As indicated above, such servo systems function to sense and address TMRs by following movement of written servo tracks on the magnetic tapes. Conventional read/write heads, however, have limited bandwidth. Therefore, they are not capable of following very fast motions such as those which result from reflections (xe2x80x9cslammingxe2x80x9d) of the magnetic tape off of a fixed tape guide. As a result, xe2x80x9cservo off trackxe2x80x9d events occur wherein the servo system is unable to properly align the head with the tape. As a result, the head must back up and again attempt to perform the read or write function. This servo transient event is undesirable as it results in unnecessary use of system resources and increases the time required for the read/write process.
To address this issue, spring-loaded pads have been proposed for use as bottom flanges on each of the front guide assemblies. These flanges are typically comprised of thin foils which apply a light load (approximately 2 grams nominal per pad or 4 grams edge force) as the tape runs between the front guide assembly. These types of guide assemblies are known as xe2x80x9ccompliant guides.xe2x80x9d
A dual reel data cartridge incorporating compliant guides is shown in FIG. 1 and designated generally by reference numeral 10. Cartridge 10 defines an enclosure, not shown, in which a pair of reels 12 and 14 are supported for free rotation about substantially parallel axis. A length of magnetic tape 16 is moved along a tape path established by front guides 18 and 20. The opposite ends of guide 18 are connected to reels 12 and 14. Guides 18 and 20 each include pads 22 which, as indicated above, are thin foils which function to apply a light load on the bottom edge of tape 16 in order to register it against the respective top flanges 24 and 26 of guides 18 and 20.
It has been found, however, that while these xe2x80x9ccompliant guidesxe2x80x9d address the issue of keeping the tape registered against one edge (flanges 24 and 26), the tape is nonetheless sensitive to off-track events originating at the tape hubs 12 and 14. Moreover, the edge force required to address steering effects resulting from tolerance differentials between the hubs 12 and 14 and the base plate 28 may result in undesirable wear on the tape edge, particularly, top edge 30.
The present invention provides a data storage cartridge having an improved tape guide which overcomes the above-noted problems of durability and servo off-track events.
The present invention relates to a clearance-type tape guide for guiding a length of magnetic tape along a tape path including at least one tape reel. The tape guide has a vertical surface for slidably engaging the tape. The length of the surface of the guide that engages the tape is defined as L1. The length of the tape path from the nearest engagement surface of the tape guide to the at least one tape reel is defined as L2. According to the invention, L1xe2x89xa70.3 L2. In other embodiments of the invention, the ratio of L1 to L2 preferably is L1xe2x89xa70.5 L2, more preferably L1xe2x89xa70.7 L2, and in certain circumstances, L1 greater than L2.
The tape guide may also include a central portion for receiving a drive transducer. The guide may be formed by bending a single, flat sheet of material. Alternatively, the tape guide may be made from multiple pieces.
The present invention also includes a data storage cartridge having a cartridge housing and a pair of tape reels mounted in the housing. The recording tape is wound on the reels and extends between them along a tape path. The cartridge also has a tape guide as described above.